The invention relates generally to shift operators for speed change gearing and more specifically to a shift operator having a single shift rail and feedback assembly for use in motor vehicle drive line components such as transmissions, transfer cases, differentials and the like.
In many motor vehicle drive line components such as transfer cases, a two-speed assembly typically including a planetary gear speed reduction unit, provides a high and low speed range which provides optimum vehicle operation on conventional roads and off-road situations, respectively. When engaged, the speed reduction assembly reduces the speed of the output of the vehicle transmission by a factor of approximately three to four. Thus, while the automatic transmission operates in its normal speed range and with normal shift points, the transfer case output shaft speed and vehicle speed is correspondingly reduced. When the transfer case speed reduction assembly is disengaged or by-passed, the input and output speeds of the transfer case are the same. Such speed reduction assemblies also commonly provide a neutral position which disconnects the transmission output from the motor vehicle drive line.
The mechanism which achieves the range selection of the speed reduction assembly has many different configurations.
In U.S. Pat. No. 4,770,280 a rotating cam axially translates a cam follower and associated shift rail which correspondingly translates a clutch collar through at least one compression spring. The spring temporarily stores energy if an attempted shift results in gear clashing until synchronism is achieved and then completes the shift.
In U.S. Pat. No. 5,407,024, a dog clutch is engaged by a shift fork which includes a cam follower. The shift fork and cam follower are moved bi-directionally by a circular cam which is rotated by an electric motor through an energy storing spring. Again, if attempted engagement of two gears causes interference and clashing, the energy storing spring allows the drive motor to complete its motion and the energy stored in the spring completes the shift when gear tooth interference ceases.
As to providing feedback signals to a controller regarding the actual position of a shift fork in such a two-speed operator assembly, numerous designs provide no feedback whatsoever. Others such as U.S. Pat. No. 5,159,847 provide feedback regarding the operational state of a transfer case but such feedback is derived from the location of a part distinct from and often remote from the actual shift fork. In U.S. Pat. No. 5,052,245, a position sensor is operably disposed adjacent a shift rail and thus provides its position, not the position of the shift fork.
It is apparent from a review of the foregoing prior art patents as well as prior art shift rail operators and sensors that improvements in these assemblies are both possible and desirable.